Polymerization reactions generally fall into one of two classes. The classes are condensation polymerizations and addition polymerizations. Common to the above-mentioned polymerization reactions is the employment of organic solvents as a medium which comprises the monomers to be polymerized and the polymer resins to be formed. Thus, the product generally obtained in polymerization reactions is polymer resins dissolved in organic solvents (hereinafter polymer resin solutions).
Additionally, polymer resins are also found solubilized in organic solvents as a result of recycling processes. For instance, a variety of waste polymer resins such as those obtained from automobile bumpers and computer casings are frequently recycled. Said waste polymer resins are often sand blasted to remove paint and subsequently ground into flakes and powders. The flakes and powders are then solubilized in organic solvents. Insolubles such as fillers, metals, paper, impact modifiers and coatings are filtered off and polymer resin solutions which often have soluble components such as dyes, stabilizers and flame retardants are obtained.
It is therefore noted that the instant novel process is effective for precipitating polymer resins as high bulk density solids from polymer resin solutions regardless of how the polymer resins originate in said solutions. Further, when said polymer resin solutions are the product of a polymerization reaction, they may often be referred to as virgin polymer resin solutions.
Many of the conventional processes utilized to isolate polymer resins from solutions are inefficient, energy intensive as well as environmentally unfavorable. This is true because the polymer resins that are isolated via conventional processes are often of low bulk density since they possess both porous particles and poor particle size distribution. In addition, they are often contaminated with low molecular weight compounds such as residual catalysts and unreacted monomers. Because of this, their chemical and physical properties (e.g., reactivity, color, odor and impact strength) are adversely altered. Moreover, conventional processes employ large volumes of volatile organic solvents as well as high energy/high temperature process steps which invariably increases the amount of organic waste polluting the environment.
It is of increasing interest to isolate polymer resins as high bulk density solids from polymer resin solutions via a process that does not adversely affect the environment. The instant invention, therefore, is based on the discovery of a novel process for isolating polymer resins as high bulk density solids from polymer resin solutions. The polymer resins possess glass transition temperatures (Tg) greater than about ambient temperature, but preferably at least about 50.degree. C. greater than ambient temperature. Additional novel embodiments of the instant invention include directly subjecting the polymer resin solutions to gaseous carbon dioxide under moderate pressures at about ambient temperature. Further, in the instant invention high bulk density is defined as about 0.2 g/cm.sup.3 to about 1.O g/cm.sup.3 but preferably about 0.3 g/cm.sup.3 to about 0.6 g/cm.sup.3. Moderate pressures are defined as about 300 psig to about 800 psig. However, a pressure of about 600 psig is often preferred.
It is noted that since the instant process is conducted at an operating temperature of about ambient temperature, the Tg values of the polymer resins isolated in the instant process are not intended to be lower than said operating temperature. Thus, said polymer resins are by definition glassy polymer resins and not rubbery polymer resins at about ambient temperature. Additionally, the Tg values of said polymer resins will increase when they are isolated from the solution and dried since organic solvents typically lower the Tg values of polymer resins.